The skin consists of a number of overlapping layers of cells. The outermost layer of the skin is called the stratum corneum and consists of dead keratinized cells. This layer protects the skin from physical and atmospheric harm, acting as a barrier to external dangers. The stratum corneum compared with the lower layers of the epidermis, is rather dry. Lack of moisture in the lower layers of the skin results in a wrinkled and aged look. Lack of moisture in the stratum corneum, however, is even more noticeable in that this is the layer that we see. The dryness is marked by roughness, increased flakiness, and in more severe cases, cracks and actual peeling. The skin may appear reddened and even inflamed if the dryness is sufficiently acute. It has been shown, by at least one scientist, that the stratum corneum remains soft and pliable only as long as the moisture content exceeds 10%. Below this, the skin becomes hard and brittle and develops an opacity.
In the lower layers of the skin, degenerative changes occur with age whereby not only moisture is lacking, but also a major amount of lipoidal or fatty substances. In cosmetic practice, it is the outermost layer of the skin which can best be benefitted by application of external lotions and creams. If this outermost layer can be made to look plump, transparent and healthy, the overall skin texture will assume a more youthful appearance, however studies of the epidermis indicate that the stratum corneum is capable of absorbing and retaining only moisture. It will not accept lipid or fatty substances. Such materials used for moisturization of the skin have no direct effect whatever in increasing the hydration of the epidermal cells.
As the result of aging, exposure to various climatic conditions, such as sun and wind and other factors in addition to loss of moisture in the epidermal layers of the skin, it has been found that loss of elasticity and skin tone and texture may occur through degradation of certain complex polypeptides present in the skin such as elastin and collagen, among others.
Elastin is a highly cross-linked amino acid complex which is a major component of elastic fibers present in the skin and connective tissue of animals and which are responsible for their physiologic elasticity. In normal human skin, these elastic tissue proteins represent a relatively small fraction of the total dermal proteins but play an important role in maintaining or improving skin tone and structure.
The dense cross-linked structure of elastin makes it very difficult to solubilize, however, this has been accomplished by means of enzymes or by means of various types of hydrolytic procedures, as described, for example, in U.S. Pat. No. 4363760.
Attempts have been made to utilize elastin, particularly when solubilized by hydrolysis, as a component of cosmetic compositions. However, it has been found that elastin is only slightly absorbed by the skin and does not penetrate sufficiently to produce substantial benefits to the skin.